[ConstraintSystem] Don't record a mismatch for synthesized arguments

Without context synthesized argument would be inferred as a hole,
so let's not record any additional fixes for it if there is no way
to infer it properly from a parameter (which could also be a hole
if it is a generic parameter type).

Resolves: rdar://78781552

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -4460,6 +4460,10 @@ bool ConstraintSystem::repairFailures(
     // a conversion to another function type, see `matchFunctionTypes`.
     if (parentLoc->isForContextualType() ||
         parentLoc->isLastElement<LocatorPathElt::ApplyArgToParam>()) {
+      // If either type has a placeholder, consider this fixed.
+      if (lhs->hasPlaceholder() || rhs->hasPlaceholder())
+        return true;
+
       // If there is a fix associated with contextual conversion or
       // a function type itself, let's ignore argument failure but
       // increase a score.

test/Constraints/generics.swift

@@ -886,3 +886,22 @@ func rdar78623338() {
     // expected-note@-1 {{only concrete types such as structs, enums and classes can conform to protocols}}
   ]
 }
+
+// rdar://78781552 - crash in `getFunctionArgApplyInfo`
+func rdar78781552() {
+  struct Test<Data, Content> where Data : RandomAccessCollection {
+    // expected-note@-1 {{where 'Data' = '(((Int) throws -> Bool) throws -> [Int])?'}}
+    // expected-note@-2 {{'init(data:filter:)' declared here}}
+    // expected-note@-3 {{'Content' declared as parameter to type 'Test'}}
+    var data: [Data]
+    var filter: (Data.Element) -> Content
+  }
+
+  func test(data: [Int]?) {
+    Test(data?.filter)
+    // expected-error@-1 {{generic struct 'Test' requires that '(((Int) throws -> Bool) throws -> [Int])?' conform to 'RandomAccessCollection'}}
+    // expected-error@-2 {{generic parameter 'Content' could not be inferred}} expected-note@-2 {{explicitly specify the generic arguments to fix this issue}}
+    // expected-error@-3 {{cannot convert value of type '(((Int) throws -> Bool) throws -> [Int])?' to expected argument type '[(((Int) throws -> Bool) throws -> [Int])?]'}}
+    // expected-error@-4 {{missing argument for parameter 'filter' in call}}
+  }
+}